If you use nightingale in any language but English playback is most likely broken in the nightly version right now, see Issue #302.

Further apt should make sure nightingale gets uninstalled when you remove the gstreamer packages it depends on. Depending on the filetype you need gstreamer0.10-plugins-good, gstreamer0.10-plugins-bad or even gstreamer0.10-plugins-ugly plus their dependencies.

If that doesn't help go to Tools->Error Console after trying to play a song.